See : ENCYCLOPAEDIA OF RARE AND FAMOUS STAMPS by L.N. Williams (page 208).

THE MOST IMPORTANT IMPERFORATE MINT BLOCK OF THE BRITISH COMMONWEALTH.

History

This remarkable survivor from the early period of the Mauritius post office can be traced as far back as Henry J. Duveen's ownership. It is not known from whom Duveen acquired the block, although he did purchase a significant portion of Sir William B. Avery's Mauritius collection. When the Duveen collection was dispersed through private sales by Charles J. Phillips in 1922-1926, the block figured prominently among the items purchased by Arthur Hind. After Hind's death, his Mauritius was offered as the fourth part of the British Empire series conducted by H. R. Harmer of London (June 12, 1934), and the "Post Paid" block sold for the U.S. dollar equivalent of $23,688, a staggering price that eclipsed the combined figure paid for the 1p and 2p "Post Office" stamps and came close to matching the amount realized by the 1p and 2p "Post Office" combination cover. The buyer was Alfred H. Caspary, presumably in competition with Maurice Burrus and Alfred F. Lichtenstein. Although Caspary's Mauritius collection paled in comparison to the holdings of his contemporaries, Burrus and Lichtenstein - he lacked even a single example of the "Post Office" stamps - the two titans of British Empire philately must have coveted their friend's "Post Paid" block. In 1958, after Caspary's death, his Mauritius was sold by H. R. Harmer, and the "Post Paid" block was featured in color in the sale catalogue, the only item in all of the Caspary sales to receive such chromatic distinction. It realized $18,500 and soon became part of the Josiah K. Lilly collection. When Siegel sold the Lilly collection after his death, the "Post Paid" block realized $64,000 (March 16, 1967).